The present invention relates to an X-ray tomographic imaging technology, and particularly to an X-ray tomographic imaging apparatus pertinent to dual-energy imaging.
In dual-energy imaging, an image can be acquired with a specific material within a subject to be examined highlighted based on X-ray projection data for the imaged subject acquired with X-rays having two different energy spectra. Specifically, an image acquired with high-energy X-rays and that acquired with low-energy X-rays are subjected to addition/subtraction processing, whereby a dual-energy image clearly showing bones and calcified lesions or that clearly showing soft tissue can be obtained.
In performing dual-energy imaging, the projection data acquired with high-energy X-rays and those acquired with low-energy X-rays are obtained by alternately switching the tube voltage for X-rays emitted by an X-ray imaging apparatus between a high voltage and a low voltage for each scan, or by replacing an X-ray filter to change the X-ray energy. For example, Japanese Patent Application Laid Open No. 2003-244542 discloses an invention comprising displaying an image representing bones or that representing soft tissue based on an image acquired with high-energy X-rays and that acquired with low-energy X-rays. To obtain an image of bones or soft tissue, the invention employs a weighting factor that is predetermined according to atoms of bones (calcium) or the like.